Contrast Agents and Diagnostic Compositions Based on Iodine-Containing Cyanuric Acid Derivatives

ABSTRACT

The present invention relates to a class of compounds of Formula (I) and to diagnostic compositions containing such compounds where the compounds are iodine containing compounds. More specifically the iodine containing compounds are chemical compounds containing a cyanuric acid scaffolding moiety allowing for the arrangement of three iodinated phenyl groups bound thereto. The invention also relates to the use of such diagnostic compositions as contrast agents in diagnostic imaging and in particular in X-ray imaging and to contrast media containing such compounds.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a class of compounds and to diagnosticcompositions containing such compounds where the compounds are iodinecontaining compounds. More specifically the iodine containing compoundsare chemical compounds containing a cyanuric acid scaffolding moietyallowing for the arrangement of three iodinated phenyl groups boundthereto.

The invention also relates to the use of such diagnostic compositions ascontrast agents in diagnostic imaging and in particular in X-ray imagingand to contrast media containing such compounds.

DESCRIPTION OF RELATED ART

All diagnostic imaging is based on the achievement of different signallevels from different structures within the body. Thus in X-ray imagingfor example, for a given body structure to be visible in the image, theX-ray attenuation by that structure must differ from that of thesurrounding tissues. The difference in signal between the body structureand its surroundings is frequently termed contrast and much effort hasbeen devoted to means of enhancing contrast in diagnostic imaging sincethe greater the contrast between a body structure and its surroundingsthe higher the quality of the images and the greater their value to thephysician performing the diagnosis. Moreover, the greater the contrastthe smaller the body structures that may be visualized in the imagingprocedures, i.e. increased contrast can lead to increased spatialresolution.

The diagnostic quality of images is strongly dependent on the inherentnoise level in the imaging procedure, and the ratio of the contrastlevel to the noise level can thus be seen to represent an effectivediagnostic quality factor for diagnostic images.

Achieving improvement in such a diagnostic quality factor has long beenand still remains an important goal. In techniques such as X-ray,magnetic resonance imaging (MRI) and ultrasound, one approach toimproving the diagnostic quality factor has been to introduce contrastenhancing materials formulated as contrast media into the body regionbeing imaged.

Thus in X-ray early examples of contrast agents were insoluble inorganicbarium salts which enhanced X-ray attenuation in the body zones intowhich they distributed. For the last 50 years the field of X-raycontrast agents has been dominated by soluble iodine containingcompounds. Commercial available contrast media containing iodinatedcontrast agents are usually classified as ionic monomers such asdiatrizoate (marketed e.g. under the trade name Gastrografen™), ionicdimers such as ioxaglate (marketed e.g. under the trade name Hexabrix™),nonionic monomers such as iohexyl (marketed e.g. under the trade nameOmnipaque™), iopamidol (marketed e.g. under the trade name Isovue™),iomeprol (marketed e.g. under the trade name Iomeron™) and the non-ionicdimer iodixanol (marketed under the trade name and Visipaque™).

The most widely used commercial non-ionic X-ray contrast agents such asthose mentioned above are considered safe. Contrast media containingiodinated contrast agents are used in more that 20 millions of X-rayexaminations annually in the USA and the number of adverse reactions isconsidered acceptable. However, since a contrast enhanced X-rayexamination will require up to about 200 ml contrast media administeredin a total dose, there is a continuous drive to provide improvedcontrast media.

The utility of the contrast media is governed largely by its toxicity,by its diagnostic efficacy, by adverse effects it may have on thesubject to which the contrast medium is administered and by the ease ofstorage and ease of administration. Since such media are conventionallyused for diagnostic purposes rather than to achieve direct therapeuticeffect, it is generally desirable to provide media having as little aspossible effect on the various biological mechanisms of the cells or thebody as this will lead to lower toxicity and lower adverse clinicaleffect. The toxicity and adverse biological effects of a contrast mediumare contributed to by the components of the formulation medium, e.g. thesolvent or carrier as well as the contrast agent itself and itscomponents such as ions for the ionic contrast agents and also by itsmetabolites.

The major contributing factors to the toxicity of the contrast mediumare identified as the chemotoxicity of the contrast agent, theosmolality of the contrast medium and the ionic composition or lackthereof of the contrast medium.

Desirable characteristics of an iodinated contrast agent are lowtoxicity of the compound itself (chemotoxicity), low viscosity of thecontrast medium wherein the compound is dissolved, low osmolality of thecontrast medium and a high iodine content (frequently measured in giodine per ml of the formulated contrast medium for administration). Theiodinated contrast agent must also be completely soluble in theformulation medium, usually an aqueous medium and remain in solutionduring storage.

The osmolality of the commercial products, and in particular of thenon-ionic compounds is acceptable for most media containing dimers andnon-ionic monomers although there is still room for improvement. Incoronary angiography for example, injection into the circulatory systemof a bolus dose of contrast medium has caused severe side effects. Inthis procedure contrast medium rather than blood flows through thesystem for a short period of time, and differences in the chemical andphysiochemical nature of the contrast medium and the blood that itreplaces can cause undesirable adverse effects such as arrhythmias, QTprolongation and reduction in cardiac contractive force. Such effectsare seen in particular with ionic contrast agents where osmotoxiceffects are associated with hypertonicity of the injected contrastmedium. Contrast media that are isotonic or slightly hypotonic—with thebody fluids are particularly desired. Low osmolar contrast media havelow renal toxicity which is particularly desirable. The osmolality is afunction of the number of particles per volume unit of the formulatedcontrast medium. To keep the injection volume of the contrast media aslow as possible it is highly desirable to formulate contrast media withhigh concentration of iodine/ml, and still maintain the osmolality ofthe media at a low level, preferably below or close to isotonicity. Thedevelopment of non-ionic monomeric contrast agents and in particularnon-ionic bis(triiodophenyl) dimers such as iodixanol (EP patent 108638)has provided contrast media with reduced osmotoxicity allowing contrasteffective iodine concentration to be achieved with hypotonic solution,and has even allowed correction of ionic imbalance by inclusion ofplasma ions while still maintaining the contrast medium Visipaque™ atthe desired osmolality (WO 90/01194 and WO 91/13636).

The X-ray contrast media at commercial high iodine concentration haverelative high viscosity, ranging from about 15 to about 60 mPas atambient temperature. Generally, contrast media where the contrastenhancing agent is a dimer has higher viscosity than the correspondingcontrast media where the contrast enhancing agent is the monomercorresponding to the dimer. Such high viscosities pose problems to theadministrators of the contrast medium, requiring relatively large boreneedles or high applied pressure, and are particularly pronounced inpediatric radiography and in radiographic techniques which require rapidbolus administration, e.g. in angiography.

Hence there still exists a desire to develop contrast agents that solvesone or more of the problems discussed. Such agents should ideally haveimproved properties over the soluble iodine containing compounds in oneor more of the following properties: renal toxicity, osmolality,viscosity, solubility, injection volumes and attenuation/radiation dose.

SUMMARY OF THE INVENTION

The present invention provides contrast media having improved propertiesover the known media with regards to at least one of the followingcriteria osmolality (and hence the renal toxicity), viscosity andsolubility. The contrast media comprises iodine containing contrastenhancing compounds where iodine containing compounds are chemicalcompounds containing a scaffolding moiety allowing for the arrangementof three iodinated phenyl groups bound to thereto. The iodine containingcontrast enhancing compounds can be synthesized from commerciallyavailable and relatively inexpensive starting materials.

DETAILED DESCRIPTION OF THE INVENTION

The contrast enhancing compounds are synthetic chemical compounds offormula (I)

wherein each of the substituents R¹, R², R³, R⁴, R⁵ and R⁶ (hereinaftercollectively denoted R group(s)) may be the same or different and denotea hydrogen atom or a non-ionic hydrophilic moiety, provided that atleast one R group is a hydrophilic moiety or salts or optical activeisomers thereof.

The solubilizing hydrophilic moieties may be any of the non-ionizinggroups conventionally used to enhance water solubility. Suitable groupsinclude straight chain or branched chain C₁₋₁₀ alkyl groups, preferablyC₁₋₅ alkyl groups, optionally with one or more CH₂ or CH moietiesreplaced by oxygen or nitrogen atoms and optionally substituted by oneor more groups selected from oxo, hydroxyl, amino or carboxylderivative, and oxo substituted sulphur and phosphorus atoms. Particularexamples include polyhydroxyalkyl, hydroxyalkoxyalkyl andhydroxypolyalkoxyalkyl and such groups attached to the phenyl group viaan amide linkage such as hydroxyalkylaminocarbonyl,N-alkyl-hydroxyalkylaminocarbonyl and bis-hydroxyalkylaminocarbonylgroups.

In a preferred embodiment the hydrophilic moieties contain 1 to 6hydroxy groups, preferably 1 to 3 hydroxy groups e.g. groups of theformulas

—CONH—CH₂—CH₂—OH

—CONH—CH₂—CHOH—CH₂—OH

—CONH—CH—(CH₂—OH)₂

—CON—(CH₂—CH₂—OH)₂

—CONH₂

—CONHCH₃

—NHCOCH₂OH

—N(COCH₃)H

—N(COCH₃)C₁₋₃ alkyl

—N(COCH₃)-mono, bis or tris-hydroxy C₁₋₄ alkyl

—N(COCH₂OH)-mono, bis or tris-hydroxy C₁₋₄ alkyl

—N(COCH₂OH)₂

—CON(CH₂—CHOH—CH₂—OH)(CH₂—CH₂—OH)

CONH—C(CH₂—OH)₃ and

CONH—CH(CH₂—OH)(CHOH—CH₂—OH).

Preferably the R groups will be equal or different and denote one ormore moieties of the formulas —CONH—CH₂—CHOH—CH₂—OH, —CONH—CH—(CH₂—OH)₂,—CON—(CH₂—CH₂—OH)₂ or —CONH—CH₂—CHOH—CH₂—OH, —NHCOCH₂OH and—N(COCH₂OH)-mono, bis or tris-hydroxy C₁₋₄ alkyl.

Thus examples of preferred structures according to the invention includethe compounds of formulas IIa, IIb and IIc below:

The compounds of formula (I) all have cyanuric acid as the centralscaffolding. Cyanuric acid exists in two isomeric forms, the enol andthe keto form as shown by Formula (III).

By attaching iodinated phenyl to the cyanuric acid the structure islocked in its keto form. The ortho iodine atoms will force the phenylgroups out of the heterocyclic ring plane, making the molecule adopt aglobular form. Globular molecules will have an enhanced solubilitycompared with molecules with a more planar structure.

The scaffolding heterocyclic cyanuric acid will itself contribute to thesolubility of the compound of formula (I) by presenting its polarcarboxylic groups to the solvent.

At an iodine concentration of 320 mg/ml which is a common concentrationfor commercially available iodinated contrast media, the concentrationof the compound of formula (I) will be approximately 0.28 M (Molar). Thecontrast medium will also be hypoosmolar at this iodine concentration,and this is an advantageous property with regards to the nephrotoxicityof the contrast medium. It is also possible to add electrolytes to thecontrast medium to lower the cardiovascular effects as explained in WO90/01194 and WO 91/13636.

Compounds of formula (I) also comprises optical active isomers. Bothenantiomerically pure products as well as mixtures of optical isomersare included.

The compounds of the invention may be used as contrast agents and may beformulated with conventional carriers and excipients to producediagnostic contrast media.

Thus viewed from a further aspect the invention provides a diagnosticcomposition comprising a compound of formula (I) as described abovetogether with at least one physiologically tolerable carrier orexcipient, e.g. in aqueous solution for injection optionally togetherwith added plasma ions or dissolved oxygen.

The contrast agent composition of the invention may be in a ready to useconcentration or may be a concentrate form for dilution prior toadministration. Generally compositions in a ready to use form will haveiodine concentrations of at least 100 mg l/ml, preferably at least 150mg l/ml, with concentrations of at least 300 mg l/ml, e.g. 320 mg l/mlbeing preferred. The higher the iodine concentration, the higher is thediagnostic value in the form of X-ray attenuation of the contrast media.However, the higher the iodine concentration the higher is the viscosityand the osmolality of the composition. Normally the maximum iodineconcentration for a given contrast media will be determined by thesolubility of the contrast enhancing agent, e.g. the iodinated compound,and the tolerable limits for viscosity and osmolality.

For contrast media which are administered by injection or infusion, thedesired upper limit for the solution's viscosity at ambient temperature(20° C.) is about 30 mPas, however viscosities of up to 50 to 60 mPasand even more than 60 mPas can be tolerated. For contrast media given bybolus injection, e.g. in angiographic procedures, osmotoxic effects mustbe considered and preferably the osmolality should be below 1 Osm/kgH₂O, preferably below 850 mOsm/kg H₂O and more preferably about 300mOsm/kg H₂O.

With the compounds of the invention such viscosity, osmolality andiodine concentrations targets can be met. Indeed, effective iodineconcentrations can be reached with hypotonic solutions. It may thus bedesirable to make up the solution's tonicity by the addition of plasmacations so as to reduce the toxicity contribution that derives from theimbalance effects following bolus injection. Such cations will desirablybe included in the ranges suggested in WO 90/01194 and WO 91/13636.

In particular, addition of sodium and calcium ions to provide a contrastmedium isotonic with blood for all iodine concentrations are desirableand obtainable. The plasma cations may be provided in the form of saltswith physiologically tolerable counterions, e.g. chloride, sulphate,phosphate, hydrogen carbonate etc., with plasma anions preferably beingused.

The compounds of the general formula (I) can be synthesized by severalsynthetic pathways known to the skilled artisan. Trimerization ofisocyanates in the presence of a tertiary amine is one such generalpathway followed by periodination and proper functionalization.Isocyanates are available from the reaction of an aniline with phosgenefollowed by dehydrochlorination. The preparation of cyanuric acidderivatives of formula (I) can be performed according to a scheme whichinvolves the following steps:

a) converting amine(s) of formula (IV)

NH₂—Ar  (IV)

wherein Ar denotes a phenyl group substituted by R⁷ at the metapositions with phosgene in toluene to produce isocyanate of formula (V)

O═C═N—Ar  (V)

where the R⁷ groups can be the same or different and denote aminogroups, nitro groups or carboxylic acid or its derivatives such asesters and amides, followed byb) dissolving the isocyanate (V) in a polar solvent such as dimethylsulfoxide and reacting at elevated temperature to form the compound offormula (VI),

optionally followed byc) reduction of a nitro containing cyanuric acid derivative usingtraditional reduction methods, such as catalytic hydrogenation or metalreduction,followed byd) iodination of the product using traditional iodination methods tointroduce 9 iodine atoms,followed bye)functionalization of amino groups by reaction with optionally protectedhydroxylated acid chlorides, such as acetoxyacetyl chloride,followed byf) functionalization of carboxylic acid groups into optionallyhydroxylated amides using traditional methods and optionally using acidchlorides as intermediates,followed byg) optional deprotection of protective groups such as esters and ethers.

The final product is then purified by conventional methods such aspreparative HPLC.

Alternatively, the amine(s) if formula (IV) may be triiodinatedsubstituted phenyl groups, in this alternative process the iodinationstep (d) is omitted.

In step a) the starting amine material (IV) is converted into thecorresponding isocyanate (V) by treatment with a solution of phosgene intoluene according to the procedure described in Houben-Weyl: Methodender Organischen Chemie, Band E4, p. 744, Georg Thieme Verlag, New York1983. The intermediate isocyanate (V) is then in step b) dissolved indimethyl sulfoxide at a concentration of about 0.3 M and the solution isheated to about 80° C. After completion of the reaction as determined byanalysis of the reaction mixture, the product is isolated by extractiveworkup followed by purification using either recrystallization or liquidchromatography.

BRIEF DESCRIPTION OF THE EXAMPLES

The invention will hereinafter be further illustrated with thenon-limiting examples. Examples 1 to 5 describes production of compoundsof formula (I). All temperatures are in ° C.

The chemical structures of the compounds of formula (I) produced by theexamples 1 to 5 below are shown below. The group Ac in formula ofExample 2 below depicts an acetyl group.

EXAMPLES Example 1N,N′,N″-Tris-[3,5-N,N′-bis-((2,3-dihydroxypronyl)aminocarbonyl)-2,4,6-triiodophenyl]-cyanuricacid

a. 5-Amino-N,N′-bis-(2,3-diacetoxypropyl)-2,4,6-triiodoisophtalamide wassynthesized from5-amino-N,N′-bis-(2,3-dihydroxypropyl)-2,4,6-triiodoisophtalamide viaO-acetylation with acetic anhydride in pyridine according to the methoddescribed in patent WO 96/09282 (example 1g).

b.5-Isocyanato-N,N′-bis-(2,3-diacetoxypropvl)-2,4,6-triiodoisophtalamide

5-Amino-N,N′-bis-(2,3-diacetoxypropyl)-2,4,6-triiodoisophtalamide isdissolved in ethylacetate and treated with a 12 molar excess of phosgenein toluene (1.93 M solution) according to the method in example 3c.

c.N,N′,N″-Tris-[3,5-N,N′-bis-((2,3-diacetoxypropyl)aminocarbonyl)-2,4,6-triiodophenyl]-cyanuricacid

5-Isocyanato-N,N′-bis-(2,3-diacetoxy propyl)-2,4,6-triiodoisophtalamideis heated in dimethyl sulfoxide according to the procedure in example3d.

d.N,N′N″-Tris-[3,5-N,N′-bis-((2,3-dihydroxypropyl)aminocarbonyl)-2,4,6-triiodophenyl]-cyanuricacid

N,N′,N″-Tris-[3,5-N,N′-bis-((2,3-diacetoxypropyl)aminocarbonyl)-2,4,6-triiodophenyl]-cyanuricacid is hydrolyzed with a 15 molar excess of aqueous sodium hydroxide.When the hydrolysis is complete (HPLC-analysis) the mixture isneutralized to pH 5-6 with a strongly acid ion exchange resin (Amberlyst15). The resin is filtered off and the filtrate is evaporated todryness. Further purification is performed by HPLC.

Example 2N,N′,N″-Tris-[5-acetamido-3-N-(2,3-dihydroxypropyl)aminocarbonyl-2,4,6-triiodophenyl]-cyanuricacid

a. 5-Amino-3-acetamido-2,4,6-triiodobenzoic acid was prepared from3,5-diacetamidobenzoic acid according to the method of U.S. Pat. No.3,991,105

b. 5-Amino-3-acetamido-2,4,6-triidodobenzoyl chloride

5-Amino-3-acetamido-2,4,6-triiodobenzoic acid was treated with thionylchloride in dioxane at 75° C. for 2½ hours. The mixture was thenevaporated to dryness, and the residue was redissolved twice in dioxaneand evaporated to dryness. The residue was trituated with water for 15min. and filtered. The light tan coloured product was dried at 40° C. invacuo (12 torr).

c. 5-Amino-3-acetamido-N-(2,3-dihydroxypropyl)-2,4,6-triiodobenzamide

5-Amino-3-acetamido-2,4,6-triiodobenzoyl chloride is reacted with twoequivalents of 2,3-dihydroxypropylamine in dry tetrahydrofuran for 20hours at ambient temperature. The salt precipitated after standing overnight is filtered off and the filtrate evaporated to a syrup.

d. 5-Amino-3-acetamido-N-(2,3-diacetoxypropyl)-2,4,6-triiodobenzamide

5-Amino-3-acetamido-N-(2,3-dihydroxypropyl)-2,4,6-triiodobenzamide isO-acetylated according to the method in example 1a.

e.5-isocyanato-3-acetamido-N-(2,3-diacetoxypropyl)-2,4,6-triiodobenzamide

5-Amino-3-acetamido-N-(2,3-diacetoxypropyl)-2,4,6-triiodobenzamide inethyl acetate is treated with phosgene according to the method inexample 3c.

f.N,N′,N″-Tris-[5-acetamido-3-N-(2,3-diacetoxypropyl)aminocarbonyl-2,4,6-triiodophenyl]-cyanuricacid

5-isocyanato-3-acetamido-N-(2,3-diacetoxypropyl)-2,4,6-triiodobenzamideis heated in dimethyl sulfoxide according to the procedure in example3d.

g.N,N′,N″-Tris-[5-acetamido-3-N-(2,3-dihydroxypropyl)aminocarbonyl-2,4,6-triiodophenyl]-cyanuricacid

N,N′,N″-Tris-[5-acetamido-3-N-(2,3-diacetoxypropyl)aminocarbonyl-2,4,6-triiodophenyl]-cyanuricacid is hydrolyzed with a 8 molar excess of aqueous sodium hydroxide andworked up according to the method in example 1d.

Example 3N,N′,N″-Tris-[5-hydroxyacetamido-3-N-(2,3-dihydroxypropyl)-carboxamido-2,4,6-triiodophenyl]-cyanuricacid

a. 5-Amino-3-nitrobenzoic acid was synthesized from 3,5-dinitrobenzoicacid according to the procedure described in literature. (Larsen et al.J. Am. Chem. Soc. vol. 78, 3210, 1956 or U.S. Pat. No. 3,128,301).

b. Methyl-5-amino-3-nitrobenzoate

5-Amino-3-nitrobenzoic acid (18.5 g, 0.10 mol) was esterified inmethanol (160 ml) by bubbling dry hydrogen chloride into the solution.After saturation, the mixture was stirred over night at ambienttemperature. The mixture was then evaporated to a crystalline residue.This was taken up in methylene chloride and washed with diluted sodiumhydrogen carbonate solution (5%) until pH 7-8 in aqueous phase. Theorganic phase was separated, dried (MgSO₄) and the solvent evaporated.Yield: 18.6 g (94%).

¹H NMR (CDCl₃): 8.21 (t, 1H, J=1.5 Hz), 7.63 & 7.61 (2t, 2H, J₁=J₂=1.5Hz), 4.19 (br. s, 2H), 3.96 (s, 3H).

c. 5-Nitro-3-carboxymethylphenylisocyanate

Methyl-5-amino-3-nitrobenzoate (5.07 g, 25.9 mmol) was dissolved inethyl acetate (75 ml). To this solution at ambient temperature was addeddropwise a solution of phosgene in toluene (75 ml, 1.93 M) withefficient stirring. The mixture was heated slowly to distil off thesolvents. When more than 50% of the solvent mixture was distilled off,the temperature of the residue was decreased to <50° C. Then a newportion of phosgene in toluene (75 ml, 1.93 M) was added and the mixturewas again heated slowly to distil off the solvents (110-120° C.). Thisoperation took about 2 h. The last traces of solvents were thendistilled off by help of a slight vacuo (200 torr). The resulting oilyresidue was taken up in dry ether (100 ml), the solution filtered andthe solvent evaporated to give a white to yellow crystalline residue.Yield: 5.5 g (96%).

IR: 2256.5 (N═C═O str.), No N—H stretching could be detected.

¹H NMR (CDCl₃): 8.65 (t, 1H, J=1.5 Hz), 8.11 (t, 1H, J=1.5 Hz), 8.08 (t,1H, J=1.5 Hz), 3.96 (s, 3H).

The product was used directly in next step.

d. N N′,N″-Tris-[5-nitro-3-carboxymethyl-phenyl]-cyanuric acid

5-Nitro-3-carboxymethylphenylisocyanate (11.2 g, 50.4 mmol) was mixedwith dimethyl sulfoxide (10 ml) in a closed flask. The flask was heatedto 80° C. for 24 h. After cooling, the contents in the flask weretriturated with water (6 ml), filtered and dried. The product wasfurther purified by preparative HPLC. Yield: 10.2 g (91%).

¹H NMR (CD₃COCD₃): 8.87 (t, 3H, J=1.5 Hz), 8.62 (t, 3H, J=1.5 Hz), 8.49(t, 3H, J=1.5 Hz), 3.98 (s, 9H).

MS (ES⁻, m/e): 701 ([M+Cl⁻]⁻, 14%), 710 ([M+HCOO]⁻, 100%).

e. N,N′,N″-Tris-[5-nitro-3-carboxy-phenyl]-cyanuric acid

N,N′,N″-Tris-[5-nitro-3-carboxymethyl-phenyl]-cyanuric acid (6.7 g, 10.0mmol) was suspended in a mixture of dioxane (200 ml) and hydrochloricacid (2 M, 240 ml). The mixture was heated to reflux and held there for14 h. During this operation a clear colourless solution was left. Thesolution was then evaporated to dryness and the residue was purified byHPLC. Yield: 6.1 g (97%).

¹H NMR (CD₃COCD₃): 8.88 (t, 3H, J=1.5 Hz), 8.62 (t, 3H, J=1.5 Hz), 8.53(t, 3H, J=1.5 Hz), 3.58 (br. s, 3H).

MS (ES⁻, m/e): 623 ([M]⁻, 100%).

f. N,N′,N″-Tris-[5-amino-3-carboxy-2,4,6-triiodophenyl]-cyanuric acid

N,N′,N″-Tris-[5-nitro-3-carboxy-phenyl]-cyanuric acid (2.5 g, 4.1 mmol)was dissolved in a mixture of ethanol (150 ml), water (40 ml) andphosphoric acid (1.0 ml). To this solution was added Pd/C catalyst (10%,0.6 g) and the solution was hydrogenated at 60 psi in a Parr apparatus.After complete hydrogen consumption the solution was filtered throughcelite and evaporated to dryness. The product was more than 96% pureaccording to HPLC analysis and was used without further purification.

MS (ESP⁺, m/e): 534 ([M]⁺, 100%).

The product above was dissolved in water (25 ml). With efficientstirring a water solution (200 ml) of electrochemically generated IBF₄(see WO 96/09282) in 24 molar excess was added dropwise. The mixture washeated to 60° C. for 96 hours. After cooling to ambient temperature thetan coloured precipitate formed was filtered off washed with a dilutesolution of sodium hydrogensulfite (15%, 10 ml), and water (25 ml). Theproduct was purified by preparative HPLC. Yield: 2.7 g (40%).

¹H NMR (DMSO-d₆): 12.65 (br. s, 3H), 3.98 (s, 6H).

¹³C NMR (DMSO-d₆): 170.9, 150.2, 149.3, 146.0, 140.5, 89.9, 89.3, 81.4,81.0.

MS (ES⁺, m/e): 1668 ([M+H]⁺, 15%), 1541 ([M+H—I]⁺, 100%).

MS (ES⁻, m/e): 1666 ([M−H]⁻, 84%), 1622 ([M-COOH]⁻, 100%).

g. N N′,N″-Tris-[5-amino-3-chlorocarboxy-2,4,6-triiodophenyl]-cyanuricacid

N,N′,N″-Tris-[5-amino-3-carboxy-2,4,6-triiodophenyl]-cyanuric acid (1.3g, 0.78 mmol) was suspended in 1,1,1-trichloroethane (8.0 ml). A drop ofN,N-dimethyl-formamide was added followed by thionyl chloride (0.90 ml,11.7 mmol). The mixture was brought to reflux for 6 h, then stirred atambient temperature over night. The mixture was evaporated, thenco-evaporated with 1,1,1-trichloroethane (2×4 ml). The solid residue wastrituated with water (5 ml), the precipitate filtered off, washed withwater (2 ml) and dried at 40° C. in vacuo (12 torr). Yield: 1.3 g (98%).

¹H NMR (DMSO-d₆): 4.52 (br. s, 6H).

¹³C NMR (DMSO-d₆): 170.3, 170.1, 150.5, 149.9, 148.9, 145.4, 140.0,80.5, 80.2.

h.N,N′,N″-Tris-[5-amino-3-N-(3-propenyl)carboxamido-2,4,6-triiodophenyl]-cyanuricacid

N,N′,N″-Tris-[5-amino-3-chlorocarboxy-2,4,6-triiodophenyl]-cyanuric acid(1.26 g, 0.73 mmol) was dissolved in tetrahydrofuran (6 ml) andallylamine (0.49 ml, 6.9 mmol) was added dropwise with efficientstirring. The mixture was stirred at ambient temperature over night, andthen evaporated to a solid residue. This was trituated with dilutehydrochloric acid (0.5 M, 4 ml) for 15 min. The precipitate was filteredoff, washed with water (2×3 ml) and sucked dry on filter. The productwas dried at 30° C. in vacuo (12 torr) to give a tan coloured powder.Yield: 1.26 g (96%).

¹H NMR (DMSO-d₆): 8.61-8.95 (m, 3H), 5.82-6.03 (m, 3H), 5.49 (br. s,6H), 5.35 (unres. d, 3H), 5.11 (unres. d, 3H), 3.73-3.95 (m, 6H).

¹³C NMR (DMSO-d₆): 170.3, 149.6, 144.2, 139.9, 135.0, 116.7, 116.5,82.5, 81.5, 42.0.

i.N,N′,N″-Tris-[5-acetoxyacetamido-3-N-(3-propenyl)carboxamido-2,4,6-triiodophenyl]-cyanuricacid

N,N′,N″-Tris-[5-amino-3-N-(3-propenyl)carboxamido-2,4,6-triiodophenyl]-cyanuricacid (1.24 g, 0.70 mmol) was dissolved in N,N-dimethylacetamide (2.5ml). At ambient temperature and with efficient stirring, acetoxyacetylchloride (0.57 g, 4.17 mmol) was added dropwise. Stirring was continuedat ambient temperature overnight. The mixture was then poured into adilute solution of sodium hydrogen carbonate (5%, 10 ml). The tancoloured precipitate formed was filtered off, washed with water (3×5 ml)and sucked dry on filter. The product was dried to a powder at 40° C. invacuo (12 torr). Yield: 1.25 g (86%).

¹H NMR (DMSO-d₆): 10.11-10.25 (br. s:s, 3H), 8.70-9.12 (m, 3H),5.81-6.02 (m, 3H), 5.25-5.40 (over). d:s, 3H), 5.04-5.19 (overl. d:s,3H), 4.64 (s, 6H), 3.77-3.98 (m, 6H), 2.11 (s, 9H).

¹³C NMR (DMSO-d₆): 170.1, 169.4, 165.6, 155.9, 150.9, 145.3, 144.1,140.8, 134.9, 116.7, 116.5, 86.6, 62.6, 42.0, 21.9, 21.0.

j.N,N′,N″-Tris-[5-acetoxyacetamido-3-N-(2,3-dihydroxypropyl)carboxamido-2,4,6-triodophenyl]-cyanuricacid

N,N′,N″-Tris-[5-acetoxyacetamido-3-N-(3-propenyl)carboxamido-2,4,6-triiodophenyl]-cyanuricacid (56 mg, 0.027 mmol) was dissolved in a mixture of acetone/water(9/1, 4 ml). Osmium tetroxide (1.5 μmol) was added followed by4-methylmorpholine N-oxide (20 mg, 0.17 mmol) and the mixture wasstirred for 16 h at ambient temperature. A solution of sodiumhydrogensulfite (15%, 0.2 ml) was added and the mixture was evaporatedto dryness. The product was purified by preparative

HPLC. Yield: 32 mg (54%).

¹H NMR (DMSO-d₆): 10.20-10.28 (s:s, 3H), 8.44-8.92 (m:s, 3H), 4.54-4.80(m:s+s, 12H), 4.42-4.4.60 (m:s, 3H), 3.60-3.76 & 3.35-3.58 (m:s, 12H),2.11 (s, 9H).

¹³C NMR (DMSO-d₆): 170.1, 169.7, 165.7, 151.4, 145.3, 144.3, 140.8,116.3, 107.1, 102.4, 98.5, 70.6, 70.4, 70.2, 64.5, 62.6, 43.1, 21.0.

MS (ES⁺, m/e): 2209 ([M+Na]⁺, 100%), 2226 ([M+K]⁺, 18%).

k.N,N′,N″-Tris-[5-hydroxyacetamido-3-N-(2,3-dihydroxypropyl)carboxamido-2,4,6-triiodophenyl]-cyanuricacid

N,N′,N″-Tris-[5-acetoxyacetamido-3-N-(2,3-dihydroxypropyl)carboxamido-2,4,6-triiodophenyl]-cyanuricacid (17 mg, 7.8 μmol) was dissolved in a methanol/water mixture (1/4,1.5 ml) and an aqueous solution of sodium hydroxide (2M, 46 μl) wasadded at ambient temperature. After stirring for ca. 1 h the mixture wasneutralized with a strongly acidic ion exchange resin (Amberlyst 15) topH 5-6. The resin was filtered off and the aqueous solution wasevaporated to dryness. The residue was purified further by preparativeHPLC. Yield 12 mg (75%).

MS (ES⁺, m/e): 2010 ([M-3H₂O]⁺, 100%), 2026 ([M-2H₂O]⁺, 27%), 2043([M−H₂O]⁺, 4%), 2083 ([M+Na]⁺, 12%).

Example 4N,N′,N″-Tris-[5-hydroxyacetamido-3-N-(2,3-dihydroxypropyl)-carboxamido-2,4,6-triiodophenyl]-cyanuricacid a.N,N′,N″-Tris-[5-acetoxacetamido-3-chlorocarboxy-2,4,6-triiodophenyl]-cyanuricacid

N,N′,N″-Tris-[5-amino-3-chlorocarboxy-2,4,6-triiodophenyl]-cyanuric acidprepared in step 3g (0.36 g, 0.21 mmol) was dissolved in dryN,N-dimethylacetamide (2.0 ml), and with efficient stirring at ambienttemperature acetoxyacetyl chloride (0.17 ml, 1.52 mmol) was addeddropwise. The mixture was stirred over night and the poured into adilute solution of aqueous sodium hydrogencarbonate (5%, 8.0 ml). Thelight brown precipitate formed was filtered off, washed with water (2×5ml), sucked dry on filter and dried at 40° C. in vacuo (12 torr). Yield:0.40 g (95%).

¹H NMR (DMSO-d₆): 10.31 (br. s, 3H), 4.52 (s, 6H), 2.08 (s, 9H).

¹³C NMR (DMSO-d₆): 170.1, 169.9, 165.7, 157.6, 156.4, 149.7, 145.4,141.5, 80.2, 61.0, 60.7, 20.8, 20.6.

b.N,N′,N″-Tris-[5-hydroxyacetamido-3-N-(3-propenyl)carboxamido-2,4,6-triiodophenyl]-cyanuricacid

N,N′,N″-Tris-[5-acetoxyacetamido-3-chlorocarboxy-2,4,6-triiodophenyl]-cyanuricacid (0.69 g, 0.34 mmol) was dissolved in tetrahydrofuran (2.5 ml) atambient temperature. Allylamine (0.51 ml, 6.8 mmol) was added withefficient stirring. The mixture was stirred for 14 h, and thenevaporated to a solid residue. This residue was trituated for 15 min.with a dilute solution of hydrochloric acid (0.05 M, 4.0 ml). The lightbrown precipitate formed was filtered off, washed with water (2×3 ml) onfilter and sucked dry. The filtercake was dried at 40° C. in vacuo (12torr) to a light brown powder. Yield: 0.65 g (97%).

¹HNMR (DMSO-d₆): 9.75-10.02 (s:s, 3H), 8.59-9.18 (m:s, 3H), 7.28 (s,3H), 5.44-6.07 (m:s, 6H), 4.81-5.46 (m:s+s:s, 9H), 3.58-4.12 (m:s, 6H).

¹³C NMR (DMSO-d₆): 169.9, 158.9, 156.0, 150.1, 149.6, 145.5, 135.0,116.5, 82.4, 80.9, 62.3.

c.N,N′,N″-Tris-[5-hydroxyacetamido-3-N-(2,3-dihydroxypropyl)carboxamido-2,4,6-triiodophenyl]-cyanuricacid

N,N′,N″-Tris-[5-hydroxyacetamido-3-N-(3-propenyl)carboxamido-2,4,6-triiodophenyl]-cyanuricacid (56 mg, 28.6 μmol) was dissolved in an acetone/water mixture (9/1,6 ml) and treated with osmium tetroxide (1.5 μmol) and4-methylmorpholine N-oxide (20.0 mg, 172 μmol) according to theconditions in example 3j. The product was purified by preparative HPLC.Yield: 47 mg (79%).

MS (ES⁺, m/2e): 1030 ([M]²⁺, 100%).

1HNMR (DMSO-d₆): 9.84 (s, 3H), 8.42-8.87 (m, 3H), 5.10-6.00 (m, 9H),4.39-4.96 (m, 9H), 3.40-4.15 (m, 12H).

¹³CNMR (DMSO-d₆): 170.9, 170.4, 166.5, 156.8, 156.0, 151.0, 149.9,145.5, 140.0, 131.3, 120.3, 116.2, 94.4, 82.5, 70.4, 70.2, 64.8, 64.4,60.4, 60.1, 43.1, 41.4.

Example 5N,N′,N″-Tris-[5-hydroxyacetamido-3-N-(2,3-dihydroxypropyl)-carboxamido-2,4,6-triiodophenyl]-cyanuricacid

N,N′N″-Tris-[5-acetoxyacetamido-3-chlorocarboxy-2,4,6-triiodophenyl]-cyanuricacid (0.10 g, 49 μmol) obtained in example 4a was dissolved inN,N-dimethylacetamide (1.5 ml). At ambient temperature with efficientstirring 2,3-dihydroxypropylamine (0.08 g, 0.88 mmol) was added. Themixture was stirred for 48 h and then evaporated in high vacuo to asemisolid residue, which was purified by preparative HPLC. Yield: 24 mg(24%).

MS (ES⁺, m/2e): 1030 ([M]²⁺, 31%).

1. Compounds of formula (I)

wherein each of the substituents R¹, R², R³, R⁴, R⁵ and R⁶ may be thesame or different and denote a hydrogen atom or a non-ionic hydrophilicmoiety, provided that at least one R group is a hydrophilic moiety orsalts or optical active isomers thereof.
 2. Compounds as claimed inclaim 1 wherein each of R¹, R², R³, R⁴, R⁵ and R⁶ may be the same ordifferent and are a straight chain or branched chain C₁₋₁₀ alkyl groupsoptionally with one or more CH₂ or CH moieties replaced by oxygen ornitrogen atoms and optionally substituted by one or more groups selectedfrom oxo, hydroxyl, amino or carboxyl derivative, and oxo substitutedsulphur and phosphorus atoms.
 3. Compounds as claimed in claim 1 whereineach of R¹, R², R³, R⁴, R⁵ and R⁶ may be the same or different and are astraight chain or branched chain C₁₋₅ alkyl groups optionally with oneor more CH₂ or CH moieties replaced by oxygen or nitrogen atoms andoptionally substituted by one or more groups selected from oxo,hydroxyl, amino or carboxyl derivative, and oxo substituted sulphur andphosphorus atoms.
 4. Compounds as claimed in claim 1 wherein each of R¹,R²R³, R⁴, R⁵ and R⁶ are hydrophilic moieties containing 1 to 6 hydroxygroups, preferably 1 to 3 hydroxy groups.
 5. Compounds as claimed inclaim 1 wherein each of R¹, R², R³, R⁴, R⁵ and R⁶ are the same ordifferent and are selected from groups of the formulas—CONH—CH₂—CH₂—OH—CONH—CH₂—CHOH—CH₂—OH—CONH—CH—(CH₂—OH)₂—CON—(CH₂—CH₂—OH)₂—CONH₂—CONHCH₃—NHCOCH₂OH—N(COCH₃)H—N(COCH₃)C₁₋₃ alkyl—N(COCH₃)-mono, bis or tris-hydroxy C₁₋₄ alkyl—N(COCH₂OH)-mono, bis or tris-hydroxy C₁₋₄ alkyl—N(COCH₂OH)₂—CON(CH₂—CHOH—CH₂—OH)(CH₂—CH₂—OH)—CONH—C(CH₂—OH)₃ and—CONH—CH(CH₂—OH)(CHOH —CH₂—OH).
 6. Compounds as claimed in claim 1wherein each of R¹, R², R³, R⁴, R⁵ and R⁶ may be the same or differentand are polyhydroxyalkyl, hydroxyalkoxyalkyl and hydroxypolyalkoxyalkyand such groups attached to the phenyl group via an amide linkage suchas hydroxyalkylaminocarbonyl, N-alkyl-hydroxyalkylaminocarbonyl andbis-hydroxyalkylaminocarbonyl groups.
 7. Compounds as claimed in claim 1wherein each of R¹, R², R³, R⁴, R⁵ and R⁶ are the same or different andare selected from groups of the formulas —CONH—CH₂—CHOH—CH₂—OH,—CONH—CH—(CH₂—OH)₂, —CON—(CH₂—CH₂—OH)₂, —CONH—CH₂—CHOH—CH₂—OH,—NHCOCH₂OH and —N(COCH₂OH)-mono, bis or tris-hydroxy C₁₋₄ alkyl. 8.Compound as claimed in claim 1 wherein each of R¹, R², R³, R⁴, R⁵ and R⁶are equal and are —CONH—CH₂—CHOH—CH₂—OH.
 9. Compound as claimed in claim1 beingN,N′,N″-Tris-[5-hydroxyacetamido-3-N-(2,3-dihydroxypropyl)-carboxamido-2,4,6-triiodophenyl]-cyanuricacid.
 10. A diagnostic agent comprising a compound of formula (I) asdefined in claim
 1. 11. A diagnostic composition comprising a compoundof formula (I) as defined in claim 1 together with a pharmaceuticallyacceptable carrier or excipient.
 12. An X-ray diagnostic compositioncomprising a compound of formula (I) as defined in claim 1 together witha pharmaceutically acceptable carrier or excipient. 13-14. (canceled)15. A method of diagnosis comprising administration of compounds offormula (I) as defined in claim 1 to the human or animal body, examiningthe body with a diagnostic device and compiling data from theexamination.
 16. A method of imaging, specifically X-ray imaging,comprising administration of compounds of formula (I) as defined inclaim 1 to the human or animal body, examining the body with adiagnostic device and compiling data from the examination and optionallyanalysing the data.
 17. A process for the preparation of a compound offormula (I) as defined in claim 1 comprising the steps of a) convertingamine(s) of formula (IV)NH₂—Ar  (IV) wherein Ar denotes a phenyl group substituted by R⁷ at themeta positions with phosgene in toluene to produce isocyanate of formula(V)O═C═N—Ar  (V) where the R⁷ groups can be the same or different anddenote amino groups, nitro groups or carboxylic acid or its derivativessuch as esters and amides, b) dissolving the isocyanate (V) in a polarsolvent and reacting at elevated temperature to form the compound offormula (VI).

c) optionally reducing a nitro containing cyanuric acid derivative tothe corresponding amino compound, d) iodinating the product from thepreceding step by introduction of 9 iodine atoms, e) functionalizingamino groups by reaction with optionally protected hydroxylated acidchlorides, such as acetoxyacetyl chloride, and/or f) functionalizingcarboxylic acid groups into optionally hydroxylated amides, and g)optional deprotection of protective groups such as esters and ethers.